Effect of epidural anaesthesia on dorsal pedis arterial diameter and blood flow

In nine subjects the influence of low (LE: blockade at or below the umbilicus; Th. 10) and high epidural anaesthesia (HE: block above the umbilicus) on vascular tone was evaluated by high frequency ultrasound (20 mHz) determined luminal diameter and a Doppler (8 mHz) assessment of mean blood flow velocity (Vmean) in the dorsalis pedis artery. The LE was induced by 0.5% bupivacain through a catheter at L3-L4, and HE was established by further infusion. Resting blood pressure and heart rate were not affected by LE or HE. One subject developed selective thoracic anaesthesia, and another was blocked on the contralateral side only. In the seven adequately blocked subjects, the luminal diameter of the dorsalis pedis artery increased from 1.70 (1.25-1.93) to 1.90 (1.75-2.23) mm during LE (+12%) and further to 2.08 (1.83-2.96) mm during HE (22%; P < 0.05). The Vmean was similar during control (7[4-26] cm s-1) and LE (12[4-55] cm s-1), but increased during HE to 35(12-78 cm s-1 (+500%; P < 0.05). Thus, arterial blood flow was higher during LE (21[7-98] ml min-1; +263%) and HE (94[21-177] ml min-1; +1175%) than at rest (8[7-36] ml min-1; P < 0.05). This study quantified the importance of sympathetic nerve activity for vascular tone and in turn blood flow in an artery of a resting human limb, as the diameter and Vmean increased with progressive epidural anaesthesia.